Interfacial Characteristics Of Ultrasonic Assisted Laser Brazing Of Diamond Grains

Diamond has good structure and performance.Diamond is often used as a tool to process hard and brittle materials such as ceramics and sapphire.At present,laser brazing has attracted extensive attention in the preparation of single-layer diamond tools,but laser brazing is a process of rapid thermal and rapid cooling,which leads to insufficient chemical metallurgical reaction between diamond abrasive grains and brazing alloy filler,the interface between the diamond abrasive grains and brazing alloy filler is poorly combined,and the diamond holding power is generally.Therefore,this paper proposes an ultrasonic assisted laser brazing diamond abrasive grain process,the purpose of which is to improve the shortcoming of laser brazing by the cavitation of ultrasonic waves to accelerate the reaction.The main research work is as follows:(1)Based on the density functional theory of first-principles method,the formation of parameters such as enthalpy and mechanical properties of carbides Cr3C2 and Cr7C3 which may occur at the interface between diamond grains and alloy filler after laser brazing are calculated and analyzed.The results show that both Cr3C2 and Cr7C3 are stable structures,Cr3C2 is easier to form than Cr7C3,and Cr7C3 is stronger than Cr3C2.(2)Ultrasonic-assisted laser brazing and laser brazing diamond abrasive grain process experiments were carried out using Ni-Cr alloy solder as the heat source.Scanning electron microscopes(SEM),X-ray energy dispersive spectroscopy(EDS)and X-ray diffraction(XRD)were used to comparison and research on the macroscopic and microscopic properties of diamonds and carbides under different processes.The mechanism of chemical metallurgy reaction of diamond abrasive grain laser brazing interface was explored.The bonding mechanism between Ni-Cr alloy brazing alloy filler and diamond abrasive grain interface was revealed.The influencing factors and internal mechanism of ultrasonic action on microstructure change during the test were analyzed.The results show that the interfacial reaction compounds of diamond abrasive grains and Ni-Cr alloy brazing filler metal in the laser brazing process are the interface reaction compounds in the ultrasonic assisted laser brazing process are sheet-like Cr3C2 and strip-like Cr7C3.The toughness of the interface carbide layer is better under the ultrasonic assisted laser brazing process.(3)Grinding tests were carried out on the two-process brazed specimens by alumina grinding wheel on the CNC grinding machine platform.The wear morphology and wear characteristics of the two specimens during the grinding process were studied.The results show that the diamond abrasive grains under the two processes have experienced four processes:small piece crushing,large block breaking,smoothing and falling off.In particular,ultrasonic-assisted laser brazing specimens have better wear resistance and longer life.